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21-07-0238-00-0000 IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN: 21-07-0238-02-0000 Title: Initial Network Selection in WLAN Date Submitted: June, 2007 Presented at IEEE 802.21 session in ETRI Authors or Source(s): Vivek Gupta, Stephen McCann, Dave Stephenson Abstract: This provides an update on initial Network Selection procedures/flow in 802.11 network using 802.21 services.
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21-07-0238-00-0000 Comment 5583 in LB-1d Add this in Annex H8 in Draft D5.1: Network Selection in 802.11 (WLAN) using 802.21:
21-07-0238-00-0000 MIH Protocol NAP Core Network Mobile Devices with WLAN 802.21 local IS AAA Proxy 802.21 IS AAA SSPN #1 802.21 IS AAA SSPN #2 SSPN: Subscription Service Provider Network MIH: Media Independent Handover 802.21 IS: MIH Information Service NAP: Network Access Provider Internet Hotspot-2 Hotspot-1 MIH Protocol Network Selection in WLAN with 802.11 & 802.21: Fig-1 802.11u
21-07-0238-00-0000 802.21 IS (home SSPN) 802.21 IS (local Access Network) APSTA Pre-configuration Advertising protocol ID (APID) = IS Maximum acceptable length (LEN) for query responses Pre-configuration Beacon (Interworking IE, GAS:APID) Probe Request Probe Response (Interworking IE, GAS:APID) GAS initial request (request IE, APID) Query content (list of SSPNs?) Relay MIH frame (with query content) Transport method: (1) 802.3, (2) IP 802.11 802.21 GAS Initial Response (Query ID, Dialog Token, comeback delay) MIH Response (transaction ID, answer information); may be delayed until answer is ready GAS Comeback Response (Query ID, answer information) GAS Comeback Request (Query ID) Comeback delay (optional – STA to PS mode) Use Case: Query SSPN List: Fig-2 Legend
21-07-0238-00-0000 Steps in Network Selection Fig-1 shows the general topology of an 802.11 (WLAN) network operating with an 802.21 IS. The steps in Network selection as shown in Fig-2 are as follows: 1) Pre-configuration: The AP is preconfigured with advertising protocol identifier (APID) of choice and is pre-configured to use 802.21 MIIS. The AP may discover the MIIS through a variety of different mechanisms that are outside the scope of specification. The maximum length of response messages from MIIS is also set. The AP may communicate with MIIS at L2 or at L3 using a protocol defined elsewhere. 2) Discover AP/Access Network Capabilities: The AP sends out a beacon with Inter-working IE set and APID set to GAS (Generic Advertisement Service). The STA may discover access network capabilities by listening to beacons or it could also send a probe request and discover access network capabilities through the probe response. 3) Query list of SSPNs: The STA sends out a query asking for list of available SSPNs? The query is defined using an 802.21 specific MIH frame. The MIH frame is then relayed by the AP to the MIIS. Meanwhile the AP sends out the initial GAS response to the STA with initial delay (comeback delay) 4) GAS response: The MIIS interprets the query and retrieves the response either from local or remote repository. It then packs the response in an appropriate MIH frame and sends it to the AP. Subsequently when the STA sends the GAS comeback request to the AP, the AP responds with the available information in the MIH frame. The STA then retrieves the information out of the MIH frame and obtains the answer to the query.
21-07-0238-00-0000 Questions and notes What is the AP-to-IS communication? –What is the protocol used? Is it direct L2 connection, MIPSHOP, RADIUS/DIAMETER, or something else entirely? Potential resolution: 802.21 needs to create an IP-based transport protocol. –Is a query ID necessary to match STA query to IS responses? Potential resolution: AP assures that 802.21 Transaction ID is unique on a per-STA basis for a reasonable time interval, and rewrites Transaction ID if necessary for uniqueness This works as a long as transactions are not integrity protected. There is no security in state 1, so this may not be a big drawback. Does the STA need to refrain from using integrity protection in state 1? How much interpretation does AP do of MIH requests? –If none, then will any claimed frame from STA be relayed to IS? –How much of the MIH packet does the AP need to understand? Query and response should be opaque. How much of the header is necessary?
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